I see what you mean, but I don't think this is super accurate. There are similarly large (and larger) patches of blue in many paintings by Vermeer and others from the Dutch Golden Age. Ultramarine was as expensive as you, but it was demonstrably used in many paintings from the Renaissance at large. The historically expensive blue paint is not the primary thing people think about when considering this painting, nor is it the reason this painting is uniquely loved among paintings of the period.

Of course, the expensive paint is a part of the history of the period, and paintings like this one become a symbol of the period as a whole. Appreciation for the period is certainly part of the appreciation for the painting.